Double-speed synchronous dynamo-electric machine



A ril 22 1924. 1,491,451

R. w. WIESEMAN I DOUBLE SPEED SYNCHRONOUS DYNAMO ELECTRIC MACHINE Filed Dec. 5. 1921 l 1 F 1 r J N 3 8 N N 5 S N-Poles 3 N 5 N S N S ZN'Poles 1 l l F/ux Distribution Fig.2.

' N N NFole Full Speed Inventor: Robert \/-/.\/i e sem an, y W2 13AM H i s 'Attorn ey.

ZN- 'Pole Half SPQQd.

electric machine of the revolving Patented Apr. 22,1924. I

UNITED STATES I r 1,491,451 PATENT OFFICE,

EDDIE-'1 I. WIEBEKAN OF SCHENECTADY, NEW YORK, ASSIGNOR 'I'O GENERAL ELEC TRIO COMPANY, A CORPORATION OF NEW YORK.

DOUBLE-SYEED SYNOHRONOUS DYNA-KOsELECTBIC MACHINE Application filed December 5, 1921. Serial 1T0. 519,925. I

To all whom it may concern:

Be it known that I, ROBERT W. Wmsnmm, a citizen of the United States, residing at Schenectady, in the county of Schenectady, State of New York, have invented certain new and useful Improvements in Doublevalues when the machine is started as an alternatin current motor.

It is we 1 known that alternating current windings of synchronous dynamo electric machines may be provided with means for chan ing the number of poles. This feature has een pro osed for starting purposes where the mac ine is used as a motor. However, it has not been practicable to use more than'one pole connection for synchronous operation ecause the usual direct current exciting magnets do not give the proper distribution of flux for more than one pole connection. In a machine built in accordance with my invention the pole pieces are so shaped that they will roduce a good flux distribution whether use singly or in airs as a single pole. Such a machine may t erefore have two efiicient synchronous operatingispeeds.

y invention will be better understood from the following description taken in connection with the drawings in which Fig. 1 represents the circuit connections of the multipolar field of a two-speed synchronous machine embodying my invention; Fig. 2 shows the shape of the pole pieces and the flux distribution when two adjacent poles are connected to have the same polarity; Fi 3 represents the same or similar poles w on connected to have 0 posite polarities.

Referring now to ig. 1, 1 represents the shaft of a multipolar synchronous dynamo ole type. 2, 2, 2 represents a portion of t e salient polar projections of such a machine, a ortion 0 the peri hery being represente as laid out flat. Tli tions may be 4 or any multiple thereof. Alternate pairs of poles are connected toslip rings 3 and the other alternate pairs are connected to sli rings 4. The two poles which make up eac pair are oppositel wound and those connected to one set of sip rings are adapted to have their polarities reversed by reversing the current supplied thereto. The two sets of slip rings may be connected in series so ,that the current supplied to each set ofpoles will be the same. This current may be supplied from any suitable direct current source not shown. With this arrangement the field of the machine may be connected for either N poles or 2 N poles where N is any even number by simply reversing the current supplied to one set of slip rings. The lettering on the upper ends of the pole pieces indicate their polarity when the machine is connected for N poles, two adjacent pole pieces being of the same polarity and acting as a single pole while the next two pole pieces act together to form a pole of the opposite polarity. Now, by simply reversing the current supplied to slip rings 3, the polarities of the poles connected thereto are reversed and the field becomes connected for 2 N poles, adjacent poles being now of opposite polarities as'indicatcd by the lettering on the lower ends of the ole ieces. The stator windings of the mac ine ave not been shown but it will be understood that they are wound so as to be connected for either N or 2 N poles. \Vhen such a machine is started as a motor, the field circuit will be open or short circuited through a. resistance or reactance and the stator windings will be connected for 2 N poles. As soon as the machine comes up to the speed corresponding to this connection the field windings may be energized for 2 N poles if it is desired to operate with this connection. If it is desired to operate with the N pole connection which will give an gierating speed equal to twice that of the 2 pole connection, the field circuit is left connected as before and the stator windings changed over by an ap ropriate pole changing switch and when the machine comes up to approximately synchronous speed for this connection, the field may be excited for N poles. During the 2 N poles starting pee number of polar'projecriod the potential induced across the sli rings will be only half what it would be if the field windings were all connected in series to one set of slip rings as is usual. During the N pole starting period the voltage induced across each pair of sli rin s will be approximately zero because t en t e potential induced in the adjacent field poles which. are connected in the same circuit will be in opposite directions and will thus neutralize each other. It is therefore evident that the induced potential across the slip rings for such a machine is kept Within reasonable limits when the machine is started as a motor.

In order to produce a good flux distribution of the poles when connected in pairs as a single pole, I make use of the non-symmetrical shape illustrated in Figs. 2 and 3; thus each pole has a non-symmetrical pole pe riphery formed by stampin the laminations in the shape illustrate in the drawings. The pairs of poles which are to be connected to form a single pole in the N pole connection have the thick long portions of the T shaped poles towards eac other, so that while the center line of the pole'pieces proper are evenly spaced, or nearly so, the peripheries of each such pair comes rather close together and the peripheries of opposite poles in the N pole connection are fur ther apart. A air of poles thus connected for the same po arity is illustrated in Fi 2 and just above the pole pieces at 5 is ilfus trated the flux distribution curve for the poles when so connected. By making the pole pieces with non-symmetrical pole tips.

pairs with symmetrical and placing them in ossible to get tips facing each other it is approximately a sine wave istribution of the flux over the two pole ieces and therefore very good operating 0 aracteristics for the N pole connection. The only place where the flux wave deviates from a sine wave is at 6, Fig. 2, op its the air p between the two poles. urthermore, t e machine is made to operate successfully with the 2 N pole connection by makin the air gap at 7, Fig. 3, between the two poFe projections sufliciently large enough to prevent too much leakage flux between the poles when the 2 N pole connection is used. The form of the flux wave for this connection will be slightly unsymmetrical but will give very good operating characteristics.

lVhile I have described in invention in connection with a machine 0 the revolving pole type, it is evident that the same is equally applicable to a machine in which the field is stationary whether of the direct current or alternating current type. .The exact shape of the pole pieces may be varied somewhat. This will also be true in-machines with different numbers of poles and I therefore do not wish to limit my invention to the exact sha shown and described.

In accordance wit the provisions of the patent statutes I have described the principle of operation of my invention to ether with the apparatus which I now consi er to represent the best embodiment thereof, but I desire to have it understood that the apparatus shown is only illustrative and that the invention may be carried out by other means.

What I claim as new and desire to secure by Letters Patent of the United States, 1s:

1. A dynamo electric machine of the type having polar projections provided with windings ada ted to be connected for either N or 2 N pol s, N being any even number, characterized by the fact that the polar projections are shaped and arran d to give approximately a sine wave flux cfigtribution for the N pole connection.

2. A field element for a dynamo electric machine comprising a plurality of substantially equally spaced polar projections, each projection having magnetica ly non-symmetrical ole tips, said projections being arran e in pairs with ma rica ole tips facing eac other.

3. X dynamo electric machine comprising a field element having 2 N polar projections, each projection having magnetically nonsymmetrical pole tips, said rojections bein arran w1th magnetica ly symmetrica pole tips facing each other windings on said projections and means or exciting said windings whereby they may produce 2 N or N poles of alternate polarity where N is any even number.

4. In a dynamo electric machine, a field element comprising 2 N polar projections, N alternate projections having a leading pole tip of greater magnetic reluctance than the trailing pole tip and the remaining projections having a trailing pole tip of greater magnetic reluctance than the leading pole tip, exciting windings on said projections, an electric circuit supplyin alternate of projections, said pairs avin the pole ti 5 of least ma etic reluctance acing each ot er, an electric circuit for suppl ing the remaining pairs of poles, said win ings being connected so that a reversal of current in one of said circuits causes said element to be changed from 2 N to N poles of alternate polarity with said pairs acting together as a single pole, N being any even number.

In witness whereof, I have hereunto se my hand this 3rd da of December, 1921.

ROBE T W. WIESEMAN.

pairs etically symmet- 

